High performance dual-layer hollow fiber fabricated via novel immiscibility induced phase separation (I ²PS) process for dehydration of ethanol

This pioneer study discloses a novel immiscibility induced phase separation (I ²PS) process to fabricate high performance dual-layer hollow fiber for dehydration of ethanol via pervaporation. The I ²PS process takes the advantages of phase separation phenomena occurring in immiscible blend dopes made of incompatible polymers. The immiscible blend dopes were simultaneously extruded through a triple orifice spinneret and fabricated into dual-layer hollow fibers consisting of an outer protective layer and an inner selective layer. A dense selective layer is formed at the outer-surface of the inner-layer due to the incompatibility between the polymer solutions of both inner and outer-layers as well as the shielding effect of the outer protective layer that provides a sufficient time for the formation of an almost defect-free selective layer during the phase inversion process. It is found that the phase inversion kinetics of the outer-layer dope solutions as well as the nature of outer-layer materials play great roles in determining the morphology of the outer protective layers and subsequently affects the permeance of the resultant hollow fibers. On the other hand, the selectivity of the as-spun fibers was found to be controlled by the outer surface of the inner-layer. The novel dual-layer hollow fiber spun from the combination of cellulose triacetate (CTA) and Ultem ^® possesses a high water permeance (29.33mol/m ²hkPa) or water flux (1.77kg/m ²h at 50°C) coupled with reasonable water/ethanol selectivity (824mol/mol) as compared to the pervaporation membranes available in the literatures. Heat treatment may enhance the selectivity of the aforementioned hollow fibers with some sacrifices of permeance. The present study may illuminate an innovative approach for hollow fiber fabrication in the future.